A photoresist is coated on a substrate such as semiconductor wafer, glass, ceramic or metal to have a thickness of from 0.5 to 2 .mu.m by a spin coating method or a roller coating method and thereafter subjected to heating, drying, printing of a circuit pattern through an exposure mask with radiation such as ultraviolet ray, post exposure baking if desired, and development to form an image.
This image as a mask is etched so as to effect pattern working on the substrate. Representative examples of the application field thereof include the production process of semiconductors such as IC, the production of circuit substrates such as liquid crystal and thermal head and other photofabrication process.
In the semiconductor fine working using a photoresist, accompanying the tendency towards finer dimensions, a matter of great importance is the prevention of light reflection from the substrate. For this purpose, a photoresist containing a light absorbent has been conventionally used, however, the use has a problem that the resolution is impaired. Accordingly, a method of providing a bottom anti-reflective coating (BARC) between the photoresist and the substrate has been broadly investigated. Known examples of the bottom anti-reflective coating are an inorganic coating type such as titanium, titanium dioxide, titanium nitride, chromium oxide, carbon and .alpha.-silicon, and an organic coating type comprising a light absorbent and a polymer material. The former requires equipments such as a vacuum evaporation apparatus, a CVD apparatus and a sputtering apparatus, for the coating formation. The latter does not require any particular equipment advantageously and a large number of studies are being made thereon. For example, JP-B-7-69611 (the term "JP-B" as used herein means an "examined Japanese patent publication") describes a coating comprising a condensate of a diphenylamine derivative with a formaldehyde-modified melamine resin, an alkali-soluble resin and a light absorbent, U.S. Pat. No. 5,294,680 describes a reaction product of a maleic anhydride copolymer with a diamine-type light absorbent, JP-A-6-118631 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describes a coating comprising a resin binder and a methylolmelamine-base heat cross-linking agent, JP-A-6-118656 describes an acrylic resin-type anti-reflective coating containing within the same molecule a carboxylic acid group, an epoxy group and a light absorbing group, JP-A-8-87115 describes a coating comprising methylolmelamine and a benzophenone-base light absorbent, and JP-A-8-179509 describes a coating obtained by adding a low molecular light absorbent to a polyvinyl alcohol resin.
The material for organic bottom anti-reflective coating preferably has physical properties such that it exhibits a large absorbance to radiations, it is insoluble in the photoresist solvent (not to cause intermixing with the photoresist layer), it is free from dispersion of a low molecular substance from the anti-reflective coating material to the overcoat photoresist layer during the coating or drying by heating, and it has a high dry etching rate as compared with the photoresist. These are also described, for example, in Proc. SPIE, Vol. 2195, 225-229 (1994).
However, the compounds described in the above-described patent publications fail to satisfy all these requirements and improvements have been demanded. For example, some conventional bottom anti-reflective coatings are insufficient in the light absorbing power of the binder and require separate loading of a light absorbent, and some contain a large amount of an aromatic light absorbent for increasing the absorbance but has a problem that the dry etching rate is low. Further, those having, in the cross-linking system, a functional group capable of increasing the alkali permeability such as a carboxylic acid group, are bound to a problem that when development with an alkaline aqueous solution is performed, the anti-reflective coating swells to incur the worsening of the resist pattern shape.